Rectifying apparatus of AC generator for vehicle

ABSTRACT

This invention includes an AC generator having a stator and a rotor supported by a frame, positive-side and negative-side radiation boards arranged within the frame and supporting positive-side and negative-side rectifying devices, respectively, for rectifying an AC output of the AC generator, an output terminal member penetrating the positive-side and negative-side radiation boards to be exposed to outside of the frame and electrically and mechanically connected with the positive-side radiation board, and a connection part forming member made of a material having the same coefficient of linear expansion as that of the output terminal member, a material having higher thermal conductivity than the positive-side radiation board, or a material having a lower ionization tendency than the positive-side radiation board, at a connection part of the positive-side radiation board with the output terminal member.

TECHNICAL FIELD

This invention relates to a rectifying apparatus of an AC generator forvehicle, constructed by integrally combining an AC generator provided inan automobile or the like and a rectifying apparatus for rectifying anoutput of the AC generator, and a method for manufacturing the same.

BACKGROUND ART

As a rectifying apparatus of an AC generator for vehicle of this type,there is, for example, a rectifying apparatus described inJP-A-11-220858. Such a rectifying apparatus of an AC generator forvehicle includes a positive-side radiation board with plural (forexample, four) positive-side rectifying devices mounted thereon, anegative-side radiation board with plural (for example, four)negative-side rectifying devices mounted thereon, and a terminal boardhaving a wiring member electrically connecting the rectifying deviceswith a stator winding. For heat sinks, which are radiation boards, analuminum (hereinafter referred to as Al) material of lightweight andgood radiation property is generally used. A metal plate such as an Alplate or copper plate having high thermal conductivity is formed (bydie-casting, metal plate working or the like) into a predeterminedshape. An output terminal bolt for taking out an output of the generatorto outside is pressed into and thereby electrically connected to thepositive-side radiation board, and the output terminal bolt isprotruding out of an AC generator frame. The output terminal bolt alsoserves for fixing the rectifying apparatus to the frame. Together withanother attachment bolt, it fixes the rectifying apparatus, for example,at two points. Since the AC generator frame functions as a groundingelectrode, the positive-side radiation board with the output terminalbolt and the frame are attached in the state of being electricallyinsulated, while the negative-side radiation board and the frame aredirectly attached electrically and thermally. The positive-sideradiation board and the negative-side radiation board are electricallyinsulated from each other at the parts where the output terminal boltand the attachment bolt are inserted, and are superimposed in theiraxial direction. These radiation boards share the bolts for attachmentto the frame. Since the positive-side radiation board with itstemperature rising higher than the temperature of the negative-sideradiation board is situated more closely to the center of the frame(inner side in the radial direction of the negative-side radiationboard), it takes in a cooling stream more efficiently for cooling.

The output terminal bolt is roulette-processed so that its contact areain a fitting range increases, but the radiation boards have smoothsurfaces and ordinary hole areas. Roulette-processing normally meansformation of protruding and recessed parts on a fitting surface. Whenthe bolt is pressed in, the top of the protruding part of the protrudingand recessed parts cuts into the corresponding surface, and as a part ofthe top shifts to the recessed part and flattened as a whole, thepressed side and the pressing side are tightly integrated.

Generally, the positive-side radiation board is made of an Al material,and the output terminal bolt pressed into the positive-side radiationboard and serving for electrical connection is made of a Fe material.Therefore, as a current (output current) flowing through the outputterminal bolt that is pressed in is increased, contact thermalresistance of the press-in fitting part increases, and not only thepositive-side radiation board but also the negative-side radiation boardand an insulating mold on the AC generator frame melt. There is a riskof failure in secure electrical connection.

Moreover, since the Al material has a higher ionization tendency and theoutput terminal bolt is protruding from the AC generator frame, foreignmatter such as water and cooling water easily enters the rectifyingapparatus along the output terminal bolt. There is a problem ofcorrosion and damage of the periphery of the output terminal boltfitting part.

Furthermore, in attachment to a vehicle, because of a force applied whena wiring is connected to the output terminal bolt, the press-in fittingpart on the radiation board may be easily displaced.

DISCLOSURE OF THE INVENTION

In view of the foregoing problems, it is an object of this invention tomore securely carry out electrical and mechanical connection of theradiation board and the output terminal member in the rectifyingapparatus of an AC generator for vehicle.

To achieve the foregoing object, this invention includes an AC generatorhaving a stator and a rotor supported by a frame, positive-side andnegative-side radiation boards arranged within the frame and supportingpositive-side and negative-side rectifying devices, respectively, forrectifying an AC output of the AC generator, an output terminal memberpenetrating the positive-side and negative-side radiation boards to beexposed to outside of the frame and electrically and mechanicallyconnected with the positive-side radiation board, and a connection partforming member made of a material having the same coefficient of linearexpansion as that of the output terminal member, a material havinghigher thermal conductivity than the positive-side radiation board, or amaterial having a lower ionization tendency than the positive-sideradiation board, at a connection part of the positive-side radiationboard with the output terminal member.

Moreover, as a method for manufacturing a rectifying apparatus of an ACgenerator for vehicle as described above, this invention provides amanufacturing method including covering an outer periphery of aconnection part forming member forming a connection part of apositive-side radiation board with an output terminal member, with athin metal foil made of a material having a lower melting point orsolidus temperature than the member, then using this as an insertionmember to constitute the positive-side radiation board by double-moldcasting, and melting only the metal foil at the time of the casting.

According to this invention, since the connection part forming membermade of the material having the same coefficient of linear expansion asthat of the output terminal member is provided at the connection part ofthe positive-side radiation board with the output terminal member,expansion of the contact surface in a heat cycle in the vehicleatmosphere can be prevented, that is, a good contact state of thecontact part can be maintained irrespective of the vehicle atmospheretemperature. Contact thermal resistance can be reduced and unwantedheating of the output terminal member can be restrained.

Moreover, since the connection part forming member is made of a materialhaving higher thermal conductivity than the positive-side radiationboard, heat can be prevented from staying at the connection part of thepositive-side radiation board with the output terminal member, andheating of the output terminal member can be smoothly transferred to thepositive-side radiation board.

Furthermore, since the periphery of the output terminal member, whichbecomes a contaminant entry path for salt water or the like from outsideof the AC generator, has a lower ionization tendency than thepositive-side radiation board, rusting and corrosion can be effectivelyprevented and hence thermal resistance at this part can be reduced.

Moreover, with the method for manufacturing a rectifying apparatus of anAC generator for vehicle according to this invention, a sufficientcontact area can be secured between the positive-side radiation boardand the output terminal member and the degree of adhesion can beimproved by the double mold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an AC generator for vehicle representingEmbodiment 1.

FIG. 2 is a perspective view showing a rectifying apparatus of the ACgenerator for vehicle according to Embodiment 1.

FIG. 3 is an exploded perspective view of a negative-side radiationboard of the rectifying apparatus in Embodiment 1.

FIG. 4 is an exploded perspective view of the rectifying apparatus inEmbodiment 1.

FIG. 5 is a plan view of a positive-side radiation board of therectifying apparatus in Embodiment 1.

FIG. 6 is a sectional view of the periphery of an output terminal memberof the rectifying apparatus in Embodiment 1.

FIG. 7 is a plan view showing another example of the positive-sideradiation board of the rectifying apparatus in Embodiment 1.

FIG. 8 is a plan view showing still another example of the positive-sideradiation board of the rectifying apparatus in Embodiment 1.

FIG. 9 is a sectional view of the periphery of an output terminal memberof a rectifying apparatus according to Embodiment 2.

FIG. 10 is a sectional view of the periphery of an output terminalmember of a rectifying apparatus according to Embodiment 4.

FIG. 11 is an explanatory view showing a process of manufacturing arectifying apparatus according to Embodiment 5.

FIG. 12 is a perspective view of an insertion member used in themanufacturing method of Embodiment 5.

BEST MODE FOR CARRYING OUT THE INVENTION EMBODIMENT 1

FIG. 1 is a structural view showing an AC generator for vehicle. In FIG.1, a stator 1 includes a stator core 2 and a stator coil 3 wound on thisstator core 2. A rotor 4 includes a pair of pole cores 5, 6 facing eachother, an excitation coil 7 inserted between the cores 5, 6, a rotaryshaft 8, and a slip ring 9 fixed on the rotary shaft 8. A front frame 12has an air intake hole 12 a and an air outlet hole 12 b, and a rearframe 13 has an air intake hole 13 a and an air outlet hole 13 b. Therear frame 13 is fixed on the front frame 12 by a fastening bolt 14, andthe stator 1 is supported between the front frame 12 and the rear frame13. The rotary shaft 8 is supported by the front frame 12 and the rearframe 13 via bearings 15, 16. A pulley 17 is fixed at one end of therotary shaft 8. A rectifying apparatus 40, which will be describedlater, is mounted on the rear frame 13 and connected with an outputterminal of the stator coil 3, thus converting AC generated by thestator 1 to DC. A voltage regulator 19 is mounted on the rear frame 13together with a brush holder 20. The brush holder 20 supports a brush 21so that the brush 21 is abutted against the slip ring 9.

In the AC generator for vehicle constructed as described above, acurrent is supplied to the excitation coil 7 via the brush 21 and theslip ring 9. At the same time, rotational torque of an engine istransmitted to the rotary shaft 8 via the pulley 17 and a belt (notshown), and the rotor 4 is rotationally driven. This causes the stator 1to generate AC. Then, this AC is converted to DC by the rectifyingapparatus 40.

In FIGS. 2 to 4, a negative-side radiation board 30 is made of aluminumand has plural negative-side rectifying device mounting parts 30 a,plural radiation fins 30 b and a pair of ring-shaped guide parts 30 c. Apositive-side radiation board 31 is made of aluminum and has pluralpositive-side rectifying device mounting parts 31 a, plural radiationfins 31 b and a pair of ring-shaped guide parts 31 c. A negative-siderectifying device 32 has an IC chip molded with a resin and has aprotruding stator coil connection terminal 32 a. A positive-siderectifying device 33 has an IC chip molded with a resin and has aprotruding stator coil connection terminal 33 a. A terminal stand 34 ismolded with a polyphenylene sulfide (PPS) resin and has pluralprotruding stator connection terminals 34 a, a pair of voltage regulatorconnection terminals 34 b and a pair of ring-shaped guide parts 34 c. Aguide 35 is made of a PPS resin and has a pair of ring-shaped guideparts 35 a.

Next, a method for assembling the rectifying apparatus 40 will bedescribed. First, as shown in FIG. 3, the negative-side rectifyingdevice 32 is joined by a solder 36 to each of the rectifying devicemounting parts 30 a of the negative-side radiation board 30. Similarly,the positive-side rectifying device 33 is joined by a solder to each ofthe rectifying device mounting parts 31 a of the positive-side radiationboard 31.

Then, the negative-side radiation board 30, the positive-side radiationboard 31, the terminal stand 34 and the guide 35 are superimposed oneach other, guided by their respective guide parts. An output terminalmember 38 is pressed into a hole of the guide parts to integrallyconnect the components, and an attachment bolt 39 is inserted in thehole. The rectifying apparatus 40 is thus assembled as shown in FIG. 2.

In this rectifying apparatus 40, insulating spacers 41, 42 are insertedbetween the guide parts 30 c, 31 c, thus securing insulation between thenegative-side radiation board 30 and the positive-side radiation board31. The stator connection terminals 32 a, 33 a, 34 a of thenegative-side radiation board 30, the positive-side radiation board 31and the terminal stand 34 are superimposed, forming a connection partwith the stator coil 3. Moreover, the rectifying apparatus 40 is fixedat a predetermined position on the rear frame 13 by the output terminalmember 38 and the attachment bolt 39.

In this Embodiment 1, as a connection part forming member forming aconnection part with the output terminal member 38, of the positive-sideradiation board 31 constituting the rectifying apparatus 40, aninsertion member 31 d made of a different metal is providedconcentrically with the guide part 31 c of the positive-side radiationboard 31.

That is, as shown in FIGS. 5 and 6, a connection part between thepositive-side radiation board 31 and the insertion member 31 d formed ina recessed and protruding shape to have an increased contact area isconstructed by double-mold casting. At the connection part of thealuminum positive-side radiation board 31 with the output terminalmember 38, an insertion member is provided, for example, using Feinsertion, Cu insertion, Cu—Zn insertion and the like. In these cases,an Fe bolt, Cu bolt and Cu—Zn bolt are used, respectively, as the outputterminal member 38, and the bolt is pressed into a hollow part of theinsertion member 31 d. The distal end of the bolt is exposed to outsideof the rear frame 13 and an outer conductor is connected thereto via aninsulating member 43.

With such a structure, since the insertion member 31 d embedded in thepositive-side radiation board 31 and the output terminal member 38 aremade of the same material and therefore have the same coefficient oflinear expansion, expansion of the contact surface in a heat cycle inthe vehicle atmosphere can be prevented, that is, both press-in contactsurfaces can be kept constant irrespective o f the vehicle atmospheretemperature. Contact thermal resistance is reduced and heating of theoutput terminal member can be prevented.

Moreover, as Cu or Cu(60%)—Zn(40%) based alloy having high thermalconductivity is used for the insertion member 31 d, contact thermalresistance can be reduced.

Although the outer periphery of the insertion member 31 d has a recessedand protruding cylindrical shape, other shapes may also be used. As longas a large contact area and integration of both parts are realized, theouter periphery of the insertion member 31 d can be formed in such amanner that at least a part of its circumferential contact surface isbent in an angled or rectangular shape, as shown in FIG. 7. For example,a simple columnar shape with increased friction may be used (FIG. 8). Onthe contrary, instead of the cylindrical shape, a barrel shape with itscentral part expanding in the direction of axial length or a conicalshape may be used. Since insertion casting is employed, the degree offreedom in shape is high.

Not only with the arrangement and shape of the output terminal member 38and the structure of the rectifying apparatus 40, but also in the casewhere the output terminal member protrudes in the radial direction ofthe AC generator or in the case where the rectifying apparatus has anarcuate shape, similar effects can be realized.

EMBODIMENT 2

As shown in FIG. 9, the space between the insertion member 31 d and theoutput terminal member 38 of Embodiment 1 is filled with a thermallyconductive member 44. A method of applying the thermally conductivemember 44 to the periphery of a press-in part of the output terminalmember 38 before pressing in, or a method of applying the thermallyconductive member 44 to the inner peripheral side of the insertionmember 31 d is used. By doing so, heat from the output terminal member38 can be efficiently transmitted to the positive-side radiation board31.

EMBODIMENT 3

As Cu or Cu(60%)—Zn(40%) based alloy having a low ionization tendency isused for the insertion member 31 d of Embodiment 1, rusting andcorrosion due to entry of salt water at the time of mounting theapparatus on a vehicle can be prevented, and damage to the insertionmember itself can be prevented to maintain the contact surface. If SUS(Fe—Ni—Cr alloy steel), which is highly anti-corrosive, is used as anFe-based material, similar effects can be realized.

EMBODIMENT 4

As shown in FIG. 10, the connection part between the output terminalmember 38 and the positive-side radiation board 31 is formed by a malescrew part 38 a (for example, M12). The male screw part 38 a has alarger root diameter B than an outer diameter A of an attachment malescrew part 38 b (for example, M8) of an output conductor connected witha storage battery (not shown) arranged on the periphery of the distalend of the output terminal, and is formed in such a manner that thescrewing direction of the male screw part 38 a is the reverse of thescrewing direction of the male screw part 38 b.

This enables screw fastening of the output conductor to the periphery ofthe distal end of the output terminal member 38 exposed to outside ofthe rear frame 13, after mounting the output terminal member 38 on thepositive-side radiation board 31 and mounting the rectifying apparatus40 on the rear frame 13. Moreover, since the screwing directions at twopositions provided on the output terminal member 38 are different, thescrew connection between the output terminal member 38 and thepositive-side radiation board 31 will not be loose when fastening theouter output conductor.

EMBODIMENT 5

An example of a method for manufacturing the positive-side radiationboard used in the rectifying apparatus 40 of this invention is shown inFIG. 11.

First, the insertion member 31 d having its outer periphery coated inadvance with a Zn foil 31 e of 0.1 mm or less by electrogalvanizing orgalvanizing is prepared (FIG. 12). Next, this insertion member 31 d isarranged in a die-casting mold for the positive-side radiation board 31and an Al material as the material of the positive-side radiation board31 is poured in this state, thus performing double-mold casting.

As this Al material in the die-casting method, an ADC material, which isan Al—Si based alloy, is generally used and its solidus temperature is580° C. Therefore, the melting temperature is 580° C. As the insertionmember, for example, Fe, Cu or Cu(60%)—Zn(40%) based alloy is used. Inthis case, the melting point and solidus temperature of each metal is1535° C. for Fe, 1083° C. for Cu and 905° C. for Cu(60%)—Zn(40%), whichis higher than the above-described Al melting temperature of 580° C.Therefore, the insertion member 31 d will not be melted or largelydeformed at the time of Al casting.

Moreover, since the Zn melting point is 420° C. compared with the Almelting temperature of 580° C., only the surface of the Zn foil 31 e onthe insertion member 31 d is melted at the time of Al casting andpouring. It completely covers the contact surface between thepositive-side radiation board 31 and the insertion member 31 d and fillsa minute casting space generated in the aluminum die-casting method.Therefore, the degree of adhesion by double-mold casting can beimproved.

INDUSTRIAL APPLICABILITY

This invention is used for a rectifying apparatus of an AC generator forvehicle, constructed by integrally combining an AC generator provided inan automobile or the like and a rectifying apparatus for rectifying anoutput of the AC generator.

1. A rectifying apparatus of an AC generator for a vehicle, comprising:positive-side and negative-side radiation boards arranged within a frameof the AC generator and supporting positive-side and negative-siderectifying devices, respectively, for rectifying an AC output of the ACgenerator; an output terminal member penetrating the positive-side andnegative-side radiation boards to be exposed to outside of the frame andelectrically and mechanically connected with the positive-side radiationboard; and a connection part forming member made of a material havingthe same coefficient of linear expansion as that of the output terminalmember, at a connection part of the positive-side radiation board withthe output terminal member, wherein the positive-side radiation boardincludes a plurality of radiation fins which are positioned over thepositive-side rectifying devices, and the negative-side radiation boardincludes a plurality of radiation fins which are positioned over thenegative-side rectifying devices.
 2. The rectifying apparatus of an ACgenerator for a vehicle as claimed in claim 1, wherein the connectionpart forming member is formed by an insertion member and is made of amaterial selected from Fe, Cu, and Cu(60%)—Zn(40%) based alloy,corresponding to the material of the output terminal member.
 3. Therectifying apparatus of an AC generator for a vehicle as claimed inclaim 1, wherein at least a part of a circumferential contact surface ofthe connection part forming member is bent in an angled or rectangularshape.
 4. The rectifying apparatus of an AC generator for a vehicle asclaimed in claim 1, wherein the output terminal member has a first malescrew part with which it is fastened to the positive-side radiationboard and a second male screw part with which an outer output conductoris fastened, wherein the first male screw part has a larger rootdiameter than an outer diameter of the second male screw part, and thefirst male screw part has a screwing direction that is the reverse of ascrewing direction of the second male screw part.
 5. The rectifyingapparatus of claim 1, wherein the radiation fins of the positive-sideradiation board extend in a first direction, and the radiation fins ofthe negative-side radiation board extend in a second direction, thefirst direction being opposite the second direction.
 6. A rectifyingapparatus of an AC generator for a vehicle, comprising: positive-sideand negative-side radiation boards arranged within a frame of the ACgenerator and supporting positive-side and negative-side rectifyingdevices, respectively, for rectifying an AC output of the AC generator;an output terminal member penetrating the positive-side andnegative-side radiation boards to be exposed to outside of the frame andelectrically and mechanically connected with the positive-side radiationboard; and a connection part forming member made of a material havinghigher thermal conductivity than the positive-side radiation board, at aconnection part of the positive-side radiation board with the outputterminal member, wherein the positive-side radiation board includes aplurality of radiation fins which are positioned over the positive-siderectifying devices, and the negative-side radiation board includes aplurality of radiation fins which are positioned over the negative-siderectifying devices.
 7. The rectifying apparatus of an AC generator for avehicle as claimed in claim 6, wherein the connection part formingmember is formed by an insertion member and is made of a materialselected from Cu and Cu(60%)—Zn(40%) based alloy, corresponding to thematerial of the output terminal member.
 8. The rectifying apparatus ofan AC generator for a vehicle as claimed in claim 6, wherein a spacebetween the connection part forming member and the output terminalmember is filled with a thermally conductive member.
 9. The rectifyingapparatus of claim 6, wherein the radiation fins of the positive-sideradiation board extend in a first direction, and the radiation fins ofthe negative-side radiation board extend in a second direction, thefirst direction being opposite the second direction.
 10. A rectifyingapparatus of an AC generator for a vehicle, comprising: positive-sideand negative-side radiation boards arranged within a frame of the ACgenerator and supporting positive-side and negative-side rectifyingdevices, respectively, for rectifying an AC output of the AC generator;and an output terminal member penetrating the positive-side andnegative-side radiation boards to be exposed to outside of the frame andelectrically and mechanically connected with the positive-side radiationboard, wherein a connection part forming member made of a materialhaving a lower ionization tendency than the positive-side radiationboard is provided at a connection part of the positive-side radiationboard with the output terminal member, and wherein the positive-sideradiation board includes a plurality of radiation fins which arepositioned over the positive-side rectifying devices, and thenegative-side radiation board includes a plurality of radiation finswhich are positioned over the negative-side rectifying devices.
 11. Therectifying apparatus of an AC generator for a vehicle as claimed inclaim 10, wherein the connection part forming member is formed by aninsertion member and is made of a material selected from Fe, Cu, Cu(60%)—Zn (40%) based alloy, and SUS (Fe—Ni—Cr alloy steel).
 12. Therectifying apparatus of claim 10, wherein the radiation fins of thepositive-side radiation board extend in a first direction, and theradiation fins of the negative-side radiation board extend in a seconddirection, the first direction being opposite the second direction. 13.A rectifying apparatus of an AC generator for a vehicle, comprising:positive-side and negative-side radiation boards arranged within a frameof the AC generator and supporting positive-side and negative-siderectifying devices, respectively, for rectifying an AC output of the ACgenerator; an output terminal member penetrating the positive-side andnegative-side radiation boards to be exposed to outside of the frame andelectrically and mechanically connected with the positive-side radiationboard; and a connection part forming member made of a material havinghigher thermal conductivity than the positive-side radiation board, at aconnection part of the positive-side radiation board with the outputterminal member, wherein the positive-side radiation board includes aplurality of radiation fins which extend in a first direction, and thenegative-side radiation board includes a plurality of radiation finswhich extend in a second direction, the first direction being oppositethe second direction.
 14. The rectifying apparatus of an AC generatorfor a vehicle as claimed in claim 13, wherein the connection partforming member is formed by an insertion member and is made of amaterial selected from Cu and Cu(60%)—Zn(40%) based alloy, correspondingto the material of the output terminal member.
 15. The rectifyingapparatus of an AC generator for a vehicle as claimed in claim 13,wherein a space between the connection part forming member and theoutput terminal member is filled with a thermally conductive member. 16.The rectifying apparatus of claim 13, wherein the radiation fins of thepositive-side radiation board are positioned over the positive-siderectifying devices, and the radiation fins of the negative-sideradiation board are positioned over the negative-side rectifyingdevices.
 17. A rectifying apparatus of an AC generator for a vehicle,comprising: positive-side and negative-side radiation boards arrangedwithin a frame of the AC generator and supporting positive-side andnegative-side rectifying devices, respectively, for rectifying an ACoutput of the AC generator; an output terminal member penetrating thepositive-side and negative-side radiation boards to be exposed tooutside of the frame and electrically and mechanically connected withthe positive-side radiation board; and a connection part forming membermade of a material having the same coefficient of linear expansion asthat of the output terminal member, at a connection part of thepositive-side radiation board with the output terminal member, whereinthe positive-side radiation board includes a plurality of radiation finswhich extend in a first direction, and the negative-side radiation boardincludes a plurality of radiation fins which extend in a seconddirection, the first direction being opposite the second direction. 18.The rectifying apparatus of an AC generator for a vehicle as claimed inclaim 17, wherein the connection part forming member is formed by aninsertion member and is made of a material selected from Fe, Cu, andCu(60%)—Zn(40%) based alloy, corresponding to the material of the outputterminal member.
 19. The rectifying apparatus of an AC generator for avehicle as claimed in claim 17, wherein at least a part of acircumferential contact surface of the connection part forming member isbent in an angled or rectangular shape.
 20. The rectifying apparatus ofan AC generator for a vehicle as claimed in claim 17, wherein the outputterminal member has a first male screw part with which it is fastened tothe positive-side radiation board and a second male screw part withwhich an outer output conductor is fastened, wherein the first malescrew part has a larger root diameter than an outer diameter of thesecond male screw part, and the first male screw part has a screwingdirection that is the reverse of a screwing direction of the second malescrew part.
 21. The rectifying apparatus of claim 17, wherein theradiation fins of the positive-side radiation board are positioned overthe positive-side rectifying devices, and the radiation fins of thenegative-side radiation board are positioned over the negative-siderectifying devices.
 22. A rectifying apparatus of an AC generator for avehicle comprising: positive-side and negative-side radiation boardsarranged within a frame of the AC generator and supporting positive-sideand negative-side rectifying devices, respectively, for rectifying an ACoutput of the AC generator; and an output terminal member penetratingthe positive-side and negative-side radiation boards to be exposed tooutside of the frame and electrically and mechanically connected withthe positive-side radiation board, wherein a connection part formingmember made of a material having a lower ionization tendency than thepositive-side radiation board is provided at a connection part of thepositive-side radiation board with the output terminal member, andwherein the positive-side radiation board includes a plurality ofradiation fins which extend in a first direction, and the negative-sideradiation board includes a plurality of radiation fins which extend in asecond direction, the first direction being opposite the seconddirection.
 23. The rectifying apparatus of an AC generator for a vehicleas claimed in claim 22, wherein the connection part forming member isformed by an insertion member and is made of a material selected fromFe, Cu, Cu(60%)—Zn (40%) based alloy, and SUS (Fe—Ni—Cr alloy steel).24. The rectifying apparatus of claim 22, wherein the radiation fins ofthe positive-side radiation board are positioned over the positive-siderectifying devices, and the radiation fins of the negative-sideradiation board are positioned over the negative-side rectifyingdevices.